Deficits in attentional function are associated with a variety of conditions in humans, including schizophrenia, attention-deficit disorder, as well as neuropathological (i.e., Alzheimer's disease) and normal aging. The occurrence of deficits in this context, however, has provided little information about the precise neural substrates underlying attention. Such information would provide insight into the biological bases of attentional dysfunction and possibly inform new methods of therapeutic intervention. Additionally, a better understanding of the neurobiology of attention may help identify the biological mechanisms by which stimuli are selected and gain access to further processing, such as long-term memory. In primates, a cortical network including the cingulate, frontal, and posterior parietal (PPC) cortices has been postulated to mediate attentional function. Indeed, impaired PPC function has been linked to attentional deficits in Alzheimer s disease, Parkinson s disease, schizophrenia, and dyslexia. Recent neuroanatomical studies have now identified a region in the rat brain that may be anatomically homologous to the PPC of primates. However, very few studies have addressed the specific behavioral functions of the rat PPC as it is now defined. Further understanding of PPC function in rats would allow subsequent research to take advantage of techniques more readily available in rodents (e.g., gene & protein expression) to explore the neurobiological mechanisms underlying attentional function. In the proposed research, a neural inactivation approach will be developed to more accurately ;haracterize the contribution of the rat PPC to attentional processes. Rats will be trained in a classical conditioning paradigm designed to increase attention to behaviorally-important stimuli. The PPC will be temporarily inactivated at the point in the procedures when attention is manipulated, to assess the importance of PPC function in this aspect of attentional processing. This approach will form the foundation for a more extensive research program which will explore the function of putative subregions of PPC as well as other components of the cortical attention network in different aspects of attention.